Seismic Performance Research Of Frame Structure Buildings Considering The Stairs

As the only reliable vertical evacuation channel of buildings, stairs play a veryimportant escape and rescue role when earthquakes occur. However, according to agreat deal of post-earthquake investigation and analysis of Wenchuan earthquake byexperts and scholars, stair members exhibit various forms of damage more severethan the main structure. The stairs increase structural strength and stiffness of astructure but attract seismic forces it could fail into short columns or into the slabsdue to high shear forces, into inclined beams supporting the steps a cause of highaxial forces. Besides, the stairs influence internal forces distribution of the mainstructural members connected with them. The cause of these phenomena is that manyof these structures are gravity designed and constructed in areas that are notconsidered seismic at the construction time.Stair damage of structures found in Wenchuan earthquake has caused greatattention of experts and scholars. Through a series of research, broad consensus havebeen reached on the interaction of stairs and the overall structures. Based on thoseresearch results, the Ministry of Housing and Urban-Rural Development modified theCode for Seismic Design of Building timely. The new version of code clearly requestthat “the establishment of calculation model, the necessary simplified calculation andprocessing should conform to the actual working condition of structure. The influenceof stair components should be considered in calculation”. Subsequently, the commoncivil structure design software PKPM updated to new version, adding the function ofstair input in order to consider the stair influence in computation.In this regard, two different structural models, established by PKPM2010andSAP2000respectively, are employed to consider the influence of stairs on structures.Two types of stairs are considered for the analyses: the one with steps constraint ininclined beams, and the stair composed of simply supported slabs. Vibration modes,periods, displacements, base shears and the internal forces of stair and frame components around of four models are obtained through modal analysis and spectrumanalysis respectively in this paper.The main contents of this paper include:1. According to the research results, different types and reasons of stair damagesto earthquake excitations are analyzed and summarized;2. Several kinds of aseismic calculation methods are introduced;3. Through the numerical results of SAP2000and PKPM2010, the influence ofstairs on seismic performance of frame structure is analyzed and summarized.4. According to the analysis results above, several design proposals of stairs inframe structures are proposed, for reference of further structural design.